Recording elements or media typically comprise a substrate or a support material optionally having on at least one surface thereof an image-forming layer. The elements include those intended for reflection viewing, which usually have an opaque support, and those intended for viewing by transmitted light, which usually have a transparent support.
While a wide variety of different types of image-recording elements have been proposed, there are many unsolved problems in the art and many deficiencies in the known products which have severely limited their commercial usefulness. These deficiencies vary with the type of image recording element.
Various arrangements have been proposed to improve the imaging quality of dye image receiving layers in thermal dye-transfer elements. JP 88-198,645 suggests the use of a support comprising a polyester matrix with polypropylene particles as a dye donor element. EP 582,750 suggests the use of a non-voided polyester layer on a support.
U.S. Pat. No. 5,100,862 relates to microvoided supports for dye-receiving elements used in thermal dye transfer systems. Polymeric microbeads are used as void initiators in a polymeric matrix to enable higher dye transfer efficiency. A problem exists with such support, however, in that, in order to attain the high level of voiding desirable for desired dye transfer efficiency, the volumetric loading of the microbeads needs to be above 25% by volume of the polymeric matrix. The degree of voiding is preferably from about 30 to 60 volume percent. At these levels of loading the tear strength of the film during manufacture is very low and also results in very poor manufacturing efficiency due to tearing of the support.
U.S. Pat. No. 6,096,684 relates to porous polyester films suitable as supports for receiving elements used in thermal dye transfer systems. Polymers immiscible with a polyester are used in a base layer while an adjacent layer, upon which a dye receiving layer is formed, contains a polyester containing dispersed inorganic particles as void initiators. These inorganic particles are less than 1.0 μm in size. The porosity of layer (B) is specified to be not less than 20% by volume. This support solves the problem of poor adhesion of imaging layers to a support consisting only of layer (A). This support has also been shown to be manufacturable at high efficiency. A problem exists with this support, however, in that the hardness of the inorganic void initiators results in poor contact with the dye donor element. This results in low dye transfer efficiency for elements using such supports. This problem was addressed by U.S. application Ser. No. 10/033,481 whereby the inorganic particles of layer (B) in U.S. Pat. No. 6,096,684 are replaced with polymeric microbeads. This significantly improved the dye transfer efficiency. A problem still exists with U.S. application Ser. No. 10/033,481, however, in that the support must be multi-layered, as the top porous layer tears apart when attempting to manufacture it as a single layered substrate. As stated previously, this requires that the manufacturing of such a support include co-extrusion. Again, it is desirable to extrude only a single layer when producing a substrate for thermal dye-transfer elements as this enables most manufacturing machines capable of manufacturing polyester films to produce such a substrate without the need of co-extrusion capability.
The use of immiscible polymer particles, such as olefins, in the polyester as a void initiator has been described in U.S. Pat. No. 4,187,113. This means of voiding is very robust and results in a low cost means to void polyester. The immiscible polymer may be added simultaneously with manufacturing the substrate. Such voided layers have been shown to be manufacturable as a single layered media. The use of such voided polyester layers in a thermal dye transfer imaging media has been shown to be deficient in terms of image quality. Thus the use of immiscible polymer particles does not by itself offer a solution to the problems observed with microbeads as described above.
The problem to be solved by the present invention is to formulate an opaque thermal dye transfer imaging media with a single layer substrate suitable for use in a thermal dye transfer printer, which is capable of recording images (including color images) having high optical densities, high image quality, capable of being manufactured at a relatively low cost, and capable of being produced on existing polyester film manufacturing machines without the need of co-extrusion capability.